Chemistry Marathon (HSC) (2 Viewers)

[TheOptimist]

With only less then a week remaining for Chemistry, I thought I would get you guys back into the spirit for it
Please post up any questions on here so that we could all discuss answers to them

 

[deswa1]

This is for people doing industrial chem- I won't post any more optional questions because not everyone can do them obviously but this one is fantastic and deserves to posted:

The ionisation of acetic acid can be written as CH3COOH -> <- CH3COO (-) + H (+). The equilibrium constant for this reaction is 1.8x10^-5. A 0.5mol/L solution of acetic acid is made up. Calculate the pH of the resultant solution at equilbrium.

 

[steero1]

is the ph 3.35?

 

[barbernator]

This is for people doing industrial chem- I won't post any more optional questions because not everyone can do them obviously but this one is fantastic and deserves to posted:

The ionisation of acetic acid can be written as CH3COOH -> <- CH3COO (-) + H (+). The equilibrium constant for this reaction is 1.8x10^-5. A 0.5mol/L solution of acetic acid is made up. Calculate the pH of the resultant solution at equilbrium.

pH = 12.7 ??

 

[louielouiee]

pH = 5 ?

 

[TheOptimist]

pH = 2.5228?
on a side note is it 0.5 mol/L initially or at equilibrium?

 

[TheOptimist]

Come on deswa1 quit the suspense

 

[barbernator]

pH = 2.5228?
on a side note is it 0.5 mol/L initially or at equilibrium?

Come on deswa1 quit the suspense

correctamundo, like srs my above post was a troll.

 

[TheOptimist]

correctamundo, like srs my above post was a troll.

hhahaah yeah I was like barbernator u srs bro, I almost had a heart attack

 

[Sanjeet]

This is for people doing industrial chem- I won't post any more optional questions because not everyone can do them obviously but this one is fantastic and deserves to posted:

The ionisation of acetic acid can be written as CH3COOH -> <- CH3COO (-) + H (+). The equilibrium constant for this reaction is 1.8x10^-5. A 0.5mol/L solution of acetic acid is made up. Calculate the pH of the resultant solution at equilbrium.

Anyone have a solution?

 

[barbernator]

Anyone have a solution?

1. Write out the equilibrium expression
2. We want to replace everything that is not [H+] with either [H+] or a constant
3. We know from standard ionisation that [H+] = [CH3COO-]
4. as 0.5 mol/L of Acetic acid is originally placed in the beaker, and these molecules either stay in their molecular form or ionise, we can say that [H+] + [CH3COOH] = 0.5
5. Replace all things other than [H+]
6. Solve quadratic taking the positive solution
7. Use pH = -log[H+]
8. Presto!

 

[someth1ng]

1. Write out the equilibrium expression
2. We want to replace everything that is not [H+] with either [H+] or a constant
3. We know from standard ionisation that [H+] = [CH3COO-]
4. as 0.5 mol/L of Acetic acid is originally placed in the beaker, and these molecules either stay in their molecular form or ionise, we can say that [H+] + [CH3COOH] = 0.5
5. Replace all things other than [H+]
6. Solve quadratic taking the positive solution
7. Use pH = -log[H+]
8. Presto!

lol...fuck that - won't be in the exam

 

[TheOptimist]

lol...fuck that - won't be in the exam

Consider your self unlucky, this is one of the perks in doing Industrial Chem

 

[someth1ng]

Consider your self unlucky, this is one of the perks in doing Industrial Chem

Not always a bad thing to do Forensic Chemistry. Weirdest and shittest topic but yeah, worth it now.

 

[madharris]

Is industrial chem good?
Shipwrecks is so boring imo

 

[B3A13]

Is industrial chem good?
Shipwrecks is so boring imo

Industrial chemistry, sucks it is boring.
Wish we did shipwrecks.

 

[crazy_paki123]

Is industrial chem good?
Shipwrecks is so boring imo

industrial chem = shit load to memorise :L

 

[7eleven]

So what's the answer?
I got ph=2.52(3 sig figures)

 

[cerebellum]

I also got pH = 2.52 (3 sig figs).
What else you got, bring it.

 

[madharris]

A student said that the use of ethanol as a fuel is entirely carbon neutral. Evaluate this statement with appropriate equations

Not sure how many marks but oh well, I'll try

Ethanol is a renewable resource which can be made from cellulose. Cellulose is a naturally occuring condensation polymer which makes up about 50% of the earths biomassIt is manufactured by photosynthesis in plants, fermentation then combustion in vehicles. THis means that it's 'carbon neutral':
photosynthesis: 6CO2(g) + 6H2(l)L --> 6O2(g) + C6H12O6(aq)
fermentation: C6H12O6(g) --yeast--> 2C2H5OH(aq) + 2CO2(g)
Combustion: C2H5OH(aq) + 3O2(g) --> 2CO2(g) + 3H2O(g)
The amount of CO2 released in fermentation and combustion is equimolar (not sure of this is the right word) to the CO2 absorbed in photosynthesis
However the energy in harvesting, manufacturing, transporting and disposal of the products generally comes from and gives CO2.
In the fermentation process we also only gain 15% ethanol, meaning more energy is used in the process, creating more CO2
Overall ethanol is not a carbon neutral fuel and therefore is not an energy source effective as a countermeasure to climate change. More research is needed in order to to be used as a alternative fuel source which is entirely carbon neutral.

Anyone willing to correct/add to that go ahead

Outline the changes that have occured in the atmospheric ozone concentrations above Antarctica during the past 20 years and explain how this information was obtained. - 4 marks